It’s hardly shocking that the most fully realized characters in “The Casual Vacancy,” J.K. Rowling’s first novel for adults, are the youngest.

Fats Wall, Krystal Weedon, Gaia Bawden, Andrew Price, Sukhvinder Jawanda: Even the names are vaguely reminiscent of those in her “Harry Potter” series, and when “The Casual Vacancy” focuses on these teenagers and their interactions (with one another, with their parents, with the petty hypocrisies of adult society), it takes on if not an urgency then a momentum of a kind.

The problem is that they are too infrequently at the center of this novel, which revolves around a small English town called Pagford and the political machinations that reverberate beneath its seeming picture-postcard quaintness, a quaintness at which Rowling hints without ever bringing it to life.

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The story of a battle for a seat on the Pagford Parish Council, which opens when councilor Barry Fairbrother drops dead of an aneurysm on his 19th wedding anniversary, the book aspires to be a satire of contemporary culture — complete with references to sex and drugs and the use of my favorite four-letter obscenity — but settles instead for broad caricature. That this is unsatisfying goes without saying; what’s surprising, given Rowling’s ability to spin a story, is just how unsatisfying it ultimately becomes.

I come to “The Casual Vacancy” as neither a fan nor a detractor of Rowling’s; I read the early “Harry Potter” novels, and found them perfectly pleasant, although I stopped after my son became old enough to finish the series on his own.

To be sure, I owe her a debt of gratitude for engaging him — then, as now, a reluctant reader — in the immersive experience of loving (certain) books; more than once, he and I went to a midnight release party, and five years ago, we heard Rowling read at the Kodak Theatre after the seventh and final Potter book, “Harry Potter and the Deathly Hallows,” was released.

Yet if “The Casual Vacancy” has a lesson to offer, it’s that there is not necessarily a correlation between writing for children and writing for adults. This can be an unpopular thing to say in a culture where grown-ups increasingly read young adult fiction, where authors such as Francine Prose, Carl Hiaasen and Sherman Alexie now write for younger readers, where everywhere the lines between maturity and adolescence have blurred.

What made “Harry Potter” popular, among other things, was that it was a classic melodrama, with clear demarcations of good and evil, and a quest (the search for destiny, for identity) that at some point engages everyone.

In the adult world, however — or, at least, the adult world Rowling portrays in “The Casual Vacancy” — becoming is no longer part of the equation; everyone has long since become.

That, in and of itself, is not the novel’s trouble: It’s been a theme of literature from the start. Still, to explore such issues accurately, with depth and compassion, requires nuance, which is what “The Casual Vacancy” lacks.

The book begins with Barry’s death, which is a questionable strategy; he’s as close as the novel has to a conscience, but Rowling has no choice but to express that secondhand. We hear a lot about him without having the chance to see him, except in the memories of those left behind.

Were Barry less important to the plot, this wouldn’t be so problematic, yet he is the catalyst for the entire narrative. Not only does his death create an opening on the council, it also casts in stark relief the divisions that have riven Pagford, a town caught between the old and the new England, between self-interest and the social good.

To highlight these tensions, Rowling gives us Howard Mollison, “an extravagantly obese man of 64,” who serves as “Chair of the Parish Council, and First Citizen of Pagford.” Along with his family, Mollison leads the old England faction: white, conservative and determined to disentangle Pagford from the Fields, a sprawling council estate between the town and the neighboring city of Yarvil. Opposing them is Parminder Jawanda, Sukhvinder’s mother, a Sikh physician who worked with Barry to undermine Howard’s agenda for the town.

Raised in the Fields, Barry found opportunity in Pagford; he was committed to giving others a similar chance. Chief among these others is Krystal, the street-smart daughter of a junkie. She’s a favorite of Barry’s from the girls rowing team he organized and a symbol, for both Rowling and her characters, of either possibility or danger, depending on your point of view.

If this sounds more than a little convoluted, it is. The first third of the book moves continually among Howard, Miles, Parminder and a dozen other central figures, all identified in such broad strokes that I had to keep flipping back and forth to remind myself who was who.

One of the particular pathologies of the novel is that nearly every adult male (with the exception of the sainted Barry) is brutal or weak, from Simon, a bully who beats his wife and kids, to Colin, a deputy headmaster who cowers in the sanctuary of his home. These men are despised by their children, but they are portrayed so two-dimensionally that we never feel much is at stake.

The same, it must be said, is factual of “The Casual Vacancy,” which doesn’t know what it wants to be. On the one hand, the degradations of the Fields and the resistance of the Pagford establishment offer a clear comment on vulture capitalism and the cruelties of the privileged class.

Rowling knows this story from the inside; she was once on public assistance and is a strong advocate for disadvantaged children — kids not unlike Krystal.

And yet, Rowling too is casually cruel to her characters, giving them problems they can’t surmount and then turning their lives from bad to worse, like John Irving in overdrive.

Is this a failure of the imagination? Maybe. Rowling clearly knows how to create a universe that’s compelling, consuming even, but Pagford is no such place.

Rather, it is little more than a backdrop, a stage set, its lack of depth an emblem of Rowling’s inability to engage us, to invest us sufficiently in her characters, young or otherwise, to reckon with the contrivances of her fictional world.